1. Field of the Invention
This invention relates to a phosphor, and more particularly to a barium fluorohalide phosphor.
2. Description of the Prior Art
Some kinds of phosphors emit fluorescent light when exposed to visible light or infrared rays after exposure to ionizing radiations, ultraviolet rays, cathode rays, or the like. This phenomenon is referred to as "stimulation", and the phosphor which exhibits stimulation phenomenon is referred to as "stimulable phosphor". It is known that a stimulable phosphor can be used for a radiation image storage panel. A radiation image of an object can be obtained by causing a panel of a stimulable phosphor to absorb a radiation such as X-rays transmitting through the object, and then exposing the panel of visible light or infrared rays to cause the stimulable phosphor to release the radiation energy stored therein as fluorescent light. Thus, a visible image can be observed or further recorded on a recording medium by detecting the fluroescent light.
In most cases of practical use of a radiation image storage panel, the object of the image is a human body. Accordingly, particularly when the radiation is ionizing radiations such as X-rays or .gamma.-rays, it is required for a stimulable phosphor employed in the radiation image storage panel to have a higher luminance of stimulated emission morder to decrease a does of ionizing radiations on the object is exposed.
As a stimulable phosphor, a cerium activated barium fluorohalide phosphor represented by the following formula has been known in the art (see U.S. Patent Application Ser. No. 57,091): EQU BaFX:xCe
wherein X is at least one halogen selected from the group consisting of chlorine, bromine and iodine, and x is a number satisfying the condition of 0&lt;x.ltoreq.2.times.10.sup.-1. The above cerium activated barium fluorohalide phosphor, however, is much more desired to have a higher intensity of stimulated emission in order to decrease a dose of ionizing radiations on the object exposed.